2acc0ac542
later. We still need to hunt down snippets used that are not. 1324 modified files... http://www.rockbox.org/mail/archive/rockbox-dev-archive-2008-06/0060.shtml git-svn-id: svn://svn.rockbox.org/rockbox/trunk@17847 a1c6a512-1295-4272-9138-f99709370657
121 lines
3.9 KiB
ArmAsm
121 lines
3.9 KiB
ArmAsm
/***************************************************************************
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* __________ __ ___.
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* Open \______ \ ____ ____ | | _\_ |__ _______ ___
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* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
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* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
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* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
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* \/ \/ \/ \/ \/
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* $Id$
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*
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* Copyright (C) 2004 by Jens Arnold
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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* KIND, either express or implied.
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*
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****************************************************************************/
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.section .icode,"ax",@progbits
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.align 2 /* this aligns to 2^2=4 byte bounday */
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.global _descramble
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.type _descramble,@function
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/* Descramble a block of byte data, from source to dest, processing len
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* bytes. Size only limited by the len argument. Note that len must
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* be an even multiple of 4 (something rolo_load() already assumes.
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* (Does the Archos firmware loader also require that?).
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*
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* Returns the 16-bit "sum" checksum of the descrambled data.
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*
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* Arguments:
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* r4 - source (unsigned char*)
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* r5 - dest (unsigned char*)
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* r6 - len (unsigned int)
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*
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* Register usage:
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* r0 - data
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* r1 - temp
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* r2 - checksum
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* r3 - current src address
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* r4 - source
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* r5 - dest
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* r6 - len -> source_end
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* r7 - dest_end
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* r8 - len / 4
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*/
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_descramble:
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mov.l r8,@-r15
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mov r6,r8
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shlr2 r8 /* r8 = len / 4 */
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mov r5,r7
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add r6,r7 /* dest_end = dest + len */
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add r4,r6 /* source_end = source + len */
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mov r4,r3 /* addr = source */
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mov #0,r2 /* checksum = 0 */
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.loop:
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mov.b @r3,r0 /* data = *addr */
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add r8,r3 /* addr += len / 4 */
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extu.b r0,r0 /* zero extend data byte */
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swap.b r0,r1 /* byte swap low word to temp */
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or r1,r0 /* r0's two lower bytes now identical */
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shlr r0 /* -> this equals "rotr.b r0" now */
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not r0,r0 /* negate */
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extu.b r0,r0 /* zero extend low byte (only needed for sum) */
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mov.b r0,@r5 /* *dest = data */
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add r0,r2 /* checksum += data */
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add #1,r5 /* dest++ */
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cmp/hi r3,r6 /* addr < source_end ? */
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bt .loop
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add #1,r4 /* source++ */
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mov r4,r3 /* addr = source */
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cmp/hi r5,r7 /* dest < dest_end */
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bt .loop
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/* 15 clock cycles if no reset of source address, 19 if reset,
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* avg. 16 cycles per byte. Magnus' Version needed 17-22 cycles per byte
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*/
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mov.l @r15+,r8
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rts
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extu.w r2,r0
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/* Move len bytes from source to dest (which must be suitably aligned for
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* long moves) and jump to dest + 0x200.
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*
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* Arguments:
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* r4 - source
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* r5 - dest
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* r6 - len
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*/
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.align 2
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.global _rolo_restart
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.type _rolo_restart,@function
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_rolo_restart:
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mov r5,r0
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sub r4,r0 /* r0 = dest - source */
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add #-4,r0 /* adjust for early increment */
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add r4,r6 /* r6 = source + len */
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.copy: /* loop takes 6 cycles per longword */
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mov.l @r4+,r1
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cmp/hi r4,r6
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mov.l r1,@(r0,r4)
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bt .copy
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mov.l @r5+,r0 /* start address from image */
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jmp @r0
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mov.l @r5+,r15 /* stack pointer from image */
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.end:
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.size _descramble,.end-_descramble
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